linux-kernel - Re: [PATCH 5/6] lightnvm: pblk: free up mempool allocation for erases correctly

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Date:   Tue, 3 Oct 2017 08:42:34 +0200
From:   Javier González <jg@...htnvm.io>
To:     Rakesh Pandit <rakesh@...era.com>
Cc:     Matias Bjørling <mb@...htnvm.io>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] lightnvm: pblk: free up mempool allocation for erases
 correctly

> On 2 Oct 2017, at 19.18, Rakesh Pandit <rakesh@...era.com> wrote:
> 
> On Mon, Oct 02, 2017 at 03:25:10PM +0300, Rakesh Pandit wrote:
>> On Mon, Oct 02, 2017 at 02:09:35PM +0200, Javier González wrote:
>>>> On 1 Oct 2017, at 15.25, Rakesh Pandit <rakesh@...era.com> wrote:
>>>> 
>>>> While separating read and erase mempools in 22da65a1b pblk_g_rq_cache
>>>> was used two times to set aside memory both for erase and read
>>>> requests.  Because same kmem cache is used repeatedly a single call to
>>>> kmem_cache_destroy wouldn't deallocate everything.  Repeatedly doing
>>>> loading and unloading of pblk modules would eventually result in some
>>>> leak.
>>>> 
>>>> The fix is to really use separate kmem cache and track it
>>>> appropriately.
>>>> 
>>>> Fixes: 22da65a1b ("lightnvm: pblk: decouple read/erase mempools")
>>>> Signed-off-by: Rakesh Pandit <rakesh@...era.com>
>>> 
>>> I'm not sure I follow this logic. I assume that you're thinking of the
>>> refcount on kmem_cache. During cache creation, all is good; if a
>>> different cache creation fails, destruction is guaranteed, since the
>>> refcount is 0. On tear down (pblk_core_free), we destroy the mempools
>>> associated to the caches. In this case, the refcount goes to 0 too, as
>>> we destroy the 2 mempools. So I don't see where the leak can happen. Am
>>> I missing something?
>>> 
>>> In any case, Jens reported some bugs on the mempools, where we did not
>>> guarantee forward progress. Here you can find the original discussion
>>> and the mempool audit [1]. Would be good if you reviewed these.
>>> 
>>> [1] https://www.spinics.net/lists/kernel/msg2602274.html
>> 
>> Thanks, yes makes sense to follow up in patch thread.  I will respond
>> to above questions there later today.
> 
> I wasn't thinking it right in addition to looking at test results from
> a incorrectly instrumented debugged version.
> 
> I went through the series you pointed and all seem okay to me now.
> 
> Please drop this patch.
> 

Cool.

Javier

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